Synthesis of nitriles



assess? srn'rnasis or arrange William F. Gresham, Wilmington, as, nameto E. I. du Pontde Nemours 81, Company, Wilmlngton, DeL', a corporationoi Delaware No Drawing. Original application February 21, '1948, SerialNo. 649,381. Divided and this application February E This inventionrelates to .the synthesis of nitriles, ,and more particularly to thesynthesis of nitriles from aldehydes and ammoniain the presence ofspecific catalysts. The process of the invention may be illustrated in aspecific embodiment by means of the following equation:

r Clo or Cu-Zn catalyst Ci-IaCHsCI-IO+NI-Ia+CI-I:CH:CN+Hed+I-Iz It hasbeen known heretofore-that certain aliphatic and aromatic nitriles canbepreparedby reaction between ammonia and aldehydes at elevatedtemperatures in the presence of catalysts such as thorium oxide. Theseprior art processes, however, invariably gave low yields of the desirednitriles, and accordingly they have ,notbeen commercially successful,even though the reactants are relatively inexpensive and the niti-liesthemselves are highly valuable as chemical intermediates.

An object of this invention is to provide a process whereby nitriles canbe obtained from aldehydes and ammonia in high yields. A more specificobject of the invention is to provide an improved and commerciallyfeasible process for the manufacture of propionitrile. Other objects Yof the invention will appear hereinafter.

These objects are accomplished in accordance with the invention byreacting an aldehyde of the formula R(CHO)n (R being a hydrocarbonradical containing from 1 to 8 carbonatoms, preferably 2 to 8 carbonatoms; 12 being an integerfrom 1 to 2 inclusive) with ammonia in thepresence of a metallic catalyst containing as an essential constituent amember of the class consisting of cobalt and copper, preferably as morespecifically hereinafter illustrated. Although combinations of copper,manganese and of copper and magnesium gave good results in carrying outthe invention, preferably the synthesis of nitriles is accomplished inaccordance with the invention in the presence of a specific type ofmetallic catalyst, namely a catalyst containing both copper and zinc.

The process of the invention may be carried out 24, 1948, Serial No.10,572 4 Claims. (cl. act-465.11)

cooled condenser and to distill the resulting condensate.

In certain instances the reaction product obtained in accordance withthe invention contains in addition to the nitriles certain pyridinederlvatives, the formation of.which may be suppressed through the use"01- specific catalysts, such as metallic cobalt or catalysts containingcopper and zinc in combination. By way of contrast, in the reactionbetween propionaldehyde and ammonia in the presence of alumina catalystsin the absence of these metals, virtually no propionitrile is produced,and appreciable quantities of 2-ethyl- 3,5- dimethyl pyridine aregenerally obtained; similarly, in the preparation of acetonitrile fromacetaldehyde and ammonia, appreciable uantities of alpha-picoline arethus frequently ob tained, One of the advantages of using the preferredcatalysts is that the formation of these byproducts can be prevented orsuppressed thereby.

The catalysts employed in the invention are preferably prepared by atleast partially reducing the metal oxides with hydrogen or a hydrogendonor such as methanol, care being taken to avoid excessive overheatingduring the said reduction. The method of reducing the catalyst is, infact, highly critical; i. e., for optimum results, it is necessarytoexercise careful control over the heat evolved and other variables. Forexample, with Cu-Zn catalysts, this can be accomplished conveniently byreducing the catalyst with aqueous methanol at a temperature of 330 to350 C. a

The term metallic" as employed herein signifies not only the metalsthemselves, but metals in the form of their oxides or in other similar,metalliferous, reducible forms. Expressions such as Cu-Zn mean catalystsin which the several at temperatures of about 275 to 500 0., preferablyabout 300 to 350 C. The pressure may be varied rather widely, butatmospheric pressureis generally preferred. Subatmospheric pressures mayalso be employed but they are generally not necessary.

The invention may be practiced by passing a mixture of the aldehyde andammoniaover grains of the catalyst at the aforesaid temperatures andpressures, and thereafter'separating the nitrile from the resultantreaction product; One convenient method for separating the said nltrileis to cool the reaction products by means-oi a waternamed ingredients(in this instance copper and zinc) are presentin "meta1lic form. Cu-Znor C0 catalysts, may, of course, contain in addition to the namedmetallic ingredients, various relatively inert materials, but suchmaterials are generally neither necessary nor desirable.

The mol ratio of ammoniazaldehyde initially introduced into the reactionvessel in accordance with the invention may vary widely, but isgenerally within the range of about 1:1 to 10:1. "If desired thereaction mixture may also contain water or inert gases such as nitrogen,and the like, but, with the preferred catalysts high yields areobtainable without using inert diluents.

The aldehydes which may be employed in the practice of the inventioninclude the lower aliphatic aldehydes, such as acetaldehyde,propionaldehyde, isobutyraldehyde, adipic dialdehyde. etc.; unsaturatedaldehydes, such as acrolein and methacrylaldehyde; and aromatic andnaphthenic practice of the.

aldehydes such as benzaldehyde, toluic aldehyde, cyclohexylacetaldehyde,and the like. The invention is especially valuable when employed in themanufacture of propionitrile from propionaldehyde and ammonia, orisobutyronitrile from isobutyraldehyde and ammonia.

The invention may be fllustrated further by means of the followingexamples. It is to be understood that the method of Example 1 is equallyapplicable in preparing other nitriles, particularly isobutyronitrileand benzonitrile.

Example 1.A copper-zinc catalyst of the formula .1Cuz2Zn was prepared byreducing the ignited coprecipitated oxalates (carbonates give similarresults) at 330 to 350 0., with 2% aqueous methanol until the analysisof the ofl gas indicated that the-only reactions occurringwere thepyrolysis of methanol and the reaction CO+H20- COr+Ha. -A mixture ofpropionaldehyde (space velocity, 197) and ammonia (space velocity, 800)was passed over the reduced catalyst at a temperature of 300 to 330 C.After leaving the catalyst, the gases passed through I a water-cooledcondenser, and the resulting liquid condensate. which was a mixture ofwater, nitrile, ammonia, and small quantities of byproduct amine, wasdried. This was accomplished by extracting with chloroform and addingpotassium carbonate to the chloroform layer. The resulting chloroformsolution of non-aqueous reaction products was filtered and distilled,yielding a fraction boiling at 95 to 97 0., which was relatively purepropionitrile. Another propionitrlle out, which had a boiling point of59 at 200 mm., was also obtained. The conversion of propionaldehyde topropionitrile was 77% of the theoretical, taking intoaccount furtherquantities of propionitrile isolated by redrying and redistilling theforeshot cuts obtained in the initial distillation.

Example 2.Example 1 was repeated under substantially similar conditions,using, in place of the CuzZn catalyst, the catalysts listed in thefollowing table.

Conversion of promonaldehflde and ammonia In each of the above tests asubstantial quantity of propionitrile was obtained, but in no instancewas the conversion as high as had been obtained as disclosed in Example1 with a Cu-Zn catalyst. In most of these tests one of the chiefby-products was 2-ethyl-3,5-dimethyl pyridine.

It is to be understood that the above examples are illustrative only andthat they do not necessarily limit the invention. Numerous modificationsof the invention will occur to those skilled in the art. For example,catalysts in a finely divided particulate state, suitable for use in"fluid catalyst" techniques. may be employed if desired. Any convenientmethod may be used for separating the nitrile from the reactionproducts.

The nitriles obtained in accordance with the present invention arewidely useful per ac, and are especially valuable for example, in themanufacture of acrylonitrile and methacrylonitrile, which are obtainablein high yield by passing the appropriate saturated nitriies(propionitrile and isobutyronitrile) over conventional dehydrogenationcatalysts at elevated temperatures.

This application is a division of my copending application 8. N.649,381, which was filed on February 21, 1946, now Patent No. 2,443,420,patented June 15, 1948.

Since many difl'erent embodiments of the invention may be made withoutdeparting from the spirit and scope thereof, it is to be understood thatI do not limit myself except as set forth in'the following claims.

I claim:

1. A process for preparing nitriles of the formula R(CN)n, R being ahydrocarbon radical having from 1 to 8 carbon atoms, n being an integerfrom 1 to 2 inclusive, which comprises reacting ammonia with an aldehydeof the formula R(CHO)n in the presence of a metallic cobalt catalyst ata temperature of about 275 to 500 C. and thereafter separating from theresultant reaction product the nitrile of the for- I mula R(CN)nproduced by the said reaction.

2. A process for preparing nitriles of the formula R(CN)n, R being ahydrocarbon radical having .from 1 to 8 carbon atoms, 11 being aninteger from 1 to 2 inclusive, which comprises reacting ammonia with analdehyde of the for-' mula R(CHO)n in the presence of a metallic cobaltcatalyst at atemperature of about 300 to 350 C. and thereafterseparating from the resultant reaction product the nitrile of theformula R(CN)n produced by the said reaction.

3. A process for. preparing nitriles of the formula RCN, R being ahydrocarbon radical having from 2 to 8 carbon atoms, which comprisesreacting ammonia with an aldehyde of the formula ROI-IO in the presenceof a metallic cobalt catalyst at a temperature of about 275 to 500 C.and thereafter separating from the resultant reaction product thenitrile of the formula RCN produced by the said reaction.

4. The process of claim 3 in which the said aldehyde is propionaldehydeand the said nitrile is proplonitrile.

WILLIAM F. GRESHAM.

REFERENCES CITED The following references file of this patent:

UNITED STATES PATENTS Name Date Dutcher July 18, 1946 Wagner Dec. 10,1946 FOREIGN PATENTS Country Date Great Britain Aug. 25, 1930 OTHERREFERENCES are of record in the Number Number chim. (4), vol. 27, p. 229

